In the prior state of the art there is known a method of guiding a stereotaxic instrument at a target point incorporating the employment of a stereotaxic apparatus disclosed in U.S.S.R. Inventor's Certificate No. 283,494, and a method similar to it incorporating the employment of a stereotaxic surgical apparatus disclosed in U.S. Pat. No. 3,457,922. The method in question comprises injecting a roentgenocontrast substance into the ventricles of the patient's brain, movably securing to the patient's head a stereotaxic instrument, X-raying the patient's head in two projections, identifying through the coordinate system definable by the intracerebral reference points a position of the target point in the coordinate system of the X-ray pictures, spatially locating a relative position of the target point and the stereotaxic instrument by the projections thereof on the X-ray pictures, moving the stereotaxic instrument for the purpose of assigning thereto such a spatial position as required for guiding at the target point, recurrently X-raying for the purpose of spatially locating a position of the target point and stereotaxic instrument after having it moved, and matching the stereotaxic instrument to the intracerebral space target point.
A disadvantage of the aforedescribed method consists in the low accuracy of spatially locating a position of the target point in the coordinate system involving the X-ray pictures owing to the absence of control over the orthogonality of the coordinate system involving the X-ray picture, the coordinate system defined by the intracerebral reference points and also the low accuracy of spatially locating the relative position of the target point and stereotaxic instrument by their projections on the X-ray pictures, inasmuch as it is next to impossible to guarantee the orthogonality of the coordinate system involving the stereotaxic apparatus, and by the coordinate system involving the X-ray picture. Hence, the accuracy of guiding the stereotaxic instrument at the target point will be insufficient in the above method. Another disadvantage of the method is the high degree of traumatization caused by the lengthy procedure of guiding and the necessity of exposing the patient to repeated irradiation in the course of the guiding procedure.
In the prior art there is known a method of guiding a stereotaxic instrument at a target point incorporating the employment of a stereotaxic neurosurgical apparatus disclosed in U.S. Pat. No. 3,357,431 comprising the steps of injecting an X-ray contrast substance into the ventricles of the patient's brain, movably fixing to the patient's cranium a stereotaxic instrument associated with two X-ray contrast point markers so that said markers and said stereotaxic instrument are established along the same straight line perpendicular to the mid-sagittal plane of the brain, X-raying the patient's cranium in two respectively perpendicular projections, locating by means of the coordinate system defined by the intracerebral reference points a spatial position of the target point in the coordinate system involving X-ray pictures, locating a spatial position of the target point relative to the X-ray contrast point markers, moving the stereotaxic instrument along the plane parallel to the mid-saggittal plane of the brain for the purpose of matching the projections of the X-ray contrast point markers to the projection of the target point on the profile X-ray picture and moving the stereotaxic instrument along the straight line perpendicular to the mid-saggital plane of the brain for the purpose of matching on the frontal X-ray picture the projection of the stereotaxic instrument to the projection of the plane parallel to the mid-sagittal plane of the brain and extending across the projection of the target point, and matching the stereotaxic instrument to the target point within the brain.
The guiding accuracy provided by this method is somewhat higher than that of the foregoing method, yet even this accuracy is not adequate by reason of the insufficiently high accuracy of locating, by means of the coordinate system defined by the intracerebral reference points, a spatial position of the target point in the coordinate system involving X-ray pictures since the orthogonality of the coordinate system involving the intracerebral reference points, the coordinate system involving X-ray pictures, fails to be controlled effectively. Another disadvantage of this method is the considerable traumatization resulting from the overly protracted guiding procedure. Furthermore, a disadvantage of the method described lies in the restrictions imposed on the availability of surgical access to the target point because upon matching the stereotaxic instrument to it, the instrument is capable of moving only along the plane parallel to the mid-sagittal plane of the brain.
Also known in the prior art is a method of guiding a stereotaxic instrument at a guiding point assuming the employment of a stereotaxic neurosurgery apparatus disclosed in U.S. Pat. No. 3,508,552 featuring the steps of injecting an X-ray contrast substance into the ventricles of the patient's brain, fastening to the patient's skull X-ray contrast markers made in the form of double grids with parallel rectangular passages forming a regular square pattern, X-raying the patient's skull in two respectively perpendicular projections, locating a spatial position of the target point in the coordinate system involving X-ray pictures by means of the coordinate system defined by the intracerebral reference points, determining in the grid arranged parallel to the mid-sagittal plane of the brain the specific rectangular passage having a projection thereof matched to a projection of the target point on the profile X-ray picture, determining in the grid arranged perpendicular to the mid-sagittal plane of the brain the specific rectangular passage having a projection thereof matched to a projection of the target point on the frontal X-ray picture, and adjusting the stereotaxic instrument to the target point within the brain by introducing the stereotaxic instrument through one of the specific rectangular passages of one of the grids to a depth corresponding to the distance from this grid to the other specific passage.
Disadvantages inherent in this method consist of the low accuracy of guiding a stereotaxic instrument, the objectionably high degree of traumatization and the limitations imposed on the availability of surgical access to the target point. The guiding accuracy provided by the present method is slightly lower than that of the preceding method owing to the fact that both of these methods are characterized by the insufficiently high accuracy of locating a spatial position of the target point in the coordinate system involving the X-ray pictures by means of the coordinate system defined by the intracerabral reference points, while the accuracy of matching the stereotaxic instrument to the target point is largely dependent on the dimensions of the rectangular passages and the distances between the adjacent passages. The traumatization level due to the time interval taken by the guiding procedure is somewhat lower in this method as compared to the foregoing one because the guiding procedure can be accomplished more quickly inasmuch as there is no need for repeated X-raying. The surgical access can be effected not only parallel to one plane, as in the preceding method, but parallel to two planes.
The abovementioned disadvantages are partially eliminated in a method of guiding a stereotaxic instrument at an intracerebral space target point described in a paper by T. Riechert "Die Stereotaktischen Hirnoperation", Deutsche Medischen Wissenschrift, 1959, vol. 84, pp. 1669-1683. This method contemplates injecting an X-ray contrast substance into the ventricles of the patient's brain, placing a stereotaxic apparatus on the patient's head, fastening detachable X-ray contrast markers to the patient's cranium, taking two X-ray pictures of the patient's head including an image of the intracerebral reference points under different projection conditions, locating a position of the intracerebral reference points relative to the X-ray contrast markers, locating a position of the intracerebral reference points relative to the target point, constructing an intracerebral space physical model including a point simulative of the target point and sequentially matching the stereotaxic instrument to the point of the physical model simulative of the target point and to the intracerebral space target point. PG,9
Subsequent to injecting an X-ray contrast substance the patient's head is placed movably in the stereotaxic apparatus made integral with an operation table and X-ray film holders. The base ring of the stereotaxic apparatus has four X-ray contrast point markers attached thereto and arranged along the two respectively perpendicular diameters of the ring. These markers define a coordinate system of the stereotaxic apparatus.
The injection of the X-ray contrast substance is effected through a specially drilled trepanation aperture.
The fastening of the X-ray point markers to the patient's cranium is effected by placing under X-ray control and rigidly fixing the patient's head in the stereotaxic apparatus. As this takes place, it is essential that the coordinate planes of the coordinate system defined by the intracerebral reference points be orthogonal to the planes of the X-ray films and the main rays of the X-ray tubes.
The X-ray pictures are taken simultaneously by two X-ray tubes when they are strictly centered with respect to the X-ray contrast point markers and the films.
The films obtained provide an image of the intracerebral reference points which is followed by constructing a coordinate system based on these points, determining the coordinates of the target point according to the stereotaxic atlas and plotting them on the films with allowance made for the enlargement coefficient of the films. A coordinate system of the stereotaxic apparatus is constructed by the projections of the four X-ray contrast point markers and the coordinates of the target point are determined in this system.
The intracerebral space physical model is constructed on the basis of a stereotaxic apparatus model representing an exact copy of the base ring of the stereotaxic apparatus. A point simulative of the target point is set forth in the intracerebral space physical model in the coordinate system of the stereotaxic apparatus.
The procedure of adjusting the stereotaxic instrument to the point of the intracerebral space physical model simulative of the target point is effected by transfering a guiding device with the stereotaxic instrument from the base ring of the stereotaxic apparatus onto the ring of the stereotaxic apparatus model. Making use of the available degrees of freedom of the guiding device therewith, the stereotaxic instrument is adjusted to the point simulative of the target point and this position of the stereotaxic instrument is fixed, whereafter the guiding device with the stereotaxic apparatus is again transferred onto the base ring of the stereotaxic apparatus and in the process of introducing the stereotaxic apparatus into the trepanation opening in the patient's skull the instrument is adjusted to the intracerebral space target point.
The aforedescribed method has significant disadvantages. Making X-ray films, determining the coordinates of the target point and adjusting the stereotaxic instrument thereto are to be accomplished as soon as the X-ray contrast substance is injected into the cavities of the patient's brain which causes the brain to swell and leads to a change of the spatial position of the cerebral structures relative to the intracerebral reference points as compared to their position specified in the stereotaxic atlas. Consequently, inaccuracy in the guiding procedure of the stereotaxic instrument may result. This disadvantage is also due to the necessity of very accurately placing the patient's head and centering the X-ray tubes, during which operations the coordinate planes of the coordinate system defined by the intracerebral reference points must be orthogonal to the planes of the films and the main rays of the X-ray tubes, which is impracticable in the actual conditions of neurosurgical intervention and brings about errors in the calculations.
Another disadvantage of the method described above is the high degree of traumatization. This is attributable to the necessity of rigidly fastening the patient's head, drilling a special trepanation opening for the injection of the X-ray contrast substance since with the patient's head being fastened it is impossible to inject a gasiform X-ray contrast substance through a lumbar puncture. The necessity of X-raying to check the fastening of the X-ray contrast markers to the patient's cranium and the adjustment of the stereotaxic instrument to the target point within the brain leads to a slow healing process of the operation injuries. The high degree of traumatization is produced due to the fact that the fastening of the patient's head, the injection of an X-ray contrast substance, the X-raying procedure, the handling of the films, the determination of the coordinates of the target point, the construction of the intracerebral space physical model and the adjustment of the stereotaxic instrument to the point of the physical model simulative of the target point are effected directly in the course of the neurosurgical operation, which, as a consequence, lasts not less than three hours. Throughout this time the patient is lying on the operation table with a trepanation opening.
The long duration of the operation does not permit guiding the stereotaxic instrument at more than three target points.
Further, when fastening the patient's head in the course of X-raying the contrasting qualities of the required cerebral cavities shown on the X-ray film are apt to deteriorate, which tends to complicate the identification of the intracerebral reference points to such an extent that occasionally it becomes indispensable either to utilize an X-ray contrast substance of improved contrasting qualities or to inject an X-ray contrast substance once again. Additionally, the rigid fastening of the head generally disagrees with certain patients, e.g. those suffering from epilepsy.
Other disadvantages of the aforesaid method consist in that in the X-raying process, the patient's head is placed in the stereotaxic apparatus comprising steel elements, which hamper the implementation of the X-raying process.
Further, in order to practice the method as described above it is necessary to have a specialized operating theater equipped with a special X-raying instrumentation, which can not be used for other purposes.